This invention relates to improvements in load-weight sensing systems for lift trucks and other similar load supporting apparatus. Such previous load-weight sensing systems commonly employ electrical load-weight measuring cells, sometimes referred to as strain gauges, interconnecting an underlying cantilever-type load-supporting fork blade member with an overlying simple beam-type load weighing platform. Some such prior systems, as exemplified by U.S. Pat. No. 9,316,528 and other references cited therein, use bendable elongate beam-type load-weight measuring cells. Other prior systems, as exemplified by US published patent applications 2007/0041820 A1 and 2011/0067502 A1, use other types of load-weight measuring cells. Any of such types of prior load-weight measuring cells can be used in the present invention, and are intended to be included herein.
In the present invention, the weight of the load elastically deforms the overlying load weighing platform and the underlying fork blade member downwardly in variable response to the weight of the load. However, the overlying load weighing platform is deformed downwardly differently than the underlying fork blade member, because the overlying platform is not supported in a cantilever fashion as is the underlying fork blade member. Instead the overlying platform is supported by weight-measuring cells in positions adjacent to the load weighing platform's forward and rearward extremities, respectively. This inconsistency results in stressing of the load-weighing platform as a simple beam supported at both ends, while simultaneously stressing the underlying fork blade member as a cantilever beam. Such difference in stressing causes lateral misalignments of the above-described load cells relative to the load-weighing platform, which then causes errors in the sensed load weight because the misalignments introduce load-cell-deforming stresses which are additional to the load weight-caused stresses. The purpose of the present invention is to minimize these error-causing load weight-sensing problems, as well as to minimize the adverse operational and economic effects that result from such problems, by automatically compensating for them.
The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.